This invention relates to springs and, more particularly, to composite springs made up of a tubular elastomeric body having a coil spring embedded in it.
Most composite springs include coil springs which have flat wound end turns. That is to say, each of the two outermost turns of the spring is of progressively decreasing pitch and is of sufficient length that it closes upon itself. This forms a square profiled end which tends to stabilize the spring when it is supported by conventional flat spring seats. These outermost turns, however, are essentially inactive from the standpoint of providing resilient spring effects in cooperation with the intervening portions of the elastomeric body. Consequently, it may be necessary, in some practical applications, to increase the overall length of the composite spring in order to achieve sufficient numbers of active coils. This means that the composite spring, in order to achieve satisfactory performance, may be of unsatisfactory length, or may be uneconomical to manufacture on account of the added costs associated with encasing and forming the inactive turns, or both.
Another drawback of composite springs of the type just described is that, in some applications involving restricted or confined space requirements, such as those commonly found in connection with automotive suspensions, the spring needs to be positioned and maintained at a predetermined rotative orientation with respect to its spring seats. This is commonly referred to as "clocking" the spring. This requirement is especially important in those applications where the spring is mounted between the spring seats of a wishbone or trailing arm suspension, in which the spring seats are moved with respect to one another on a pivotal linkage that causes them to compress the composite spring in non-axial directions. In these and other generally similar applications, the composite spring typically is fabricated so that its compression characteristics, when positioned at a predetermined rotative or "clock" position, counteract the nonsymmetrical bulging effects which occur as a result of the spring seat construction. Consequently, so long as the composite spring is maintained in this position, it can be compressed in a stable manner, without fears of buckling. If the spring shifts away from the predetermined "clock" position, however, the tendency for it to buckle on account of nonsymmetric loading is increased.
Still another requirement of composite springs of the type just described, as well as other tubular elastomeric springs, especially when used as the primary spring elements of automotive suspension struts, is that they cooperate with the spring seats to effectively seal the moving parts of the suspension strut against the entrance of moisture, dirt or other contaminants. The most commonly used end constructions for such springs, however, does not afford satisfactory seals for this purpose because they are formed merely to rest upon the spring seats between which the springs are mounted, and typically have square or blunted end profiles.